Agricultural covering material

ABSTRACT

The present invention provides an agricultural covering material comprising a fluororesin film which intercepts the transmission of the ultraviolet rays having a wavelength range of at least 300-330 nm, by at least 40% and which transmits at least 70% of the visible rays having a wavelength range of 400-800 nm. 
     The covering material can be used outdoors in a spread state over a long period of time and is useful as a covering material for greenhouse to replace glass, for cultivation of various useful crops.

TECHNICAL FIELD

The present invention relates to an agricultural covering material,particularly to an agricultural covering material which partiallyintercepts the rays of particular wavelength ranges and which can beused in a spread state over a long period of time.

BACKGROUND ART

There have been used, as covering materials for plastic tunnel or pipehouse, a polyethylene film, an ethylene-vinyl acetate copolymer film, apolyester film, a vinyl chloride resin film, etc. A vinyl chloride resinfilm occupies a major portion because of the applicability, price,heat-insulatability, etc. Since these resins have inferior outdoordurability, they are used for 1-2 years and farmers replace the coveringmaterials every 1-2 years.

Full-scale large houses have been used in recent years for the purposesof labor saving for house management, enlargement of cultivation area,cultivation of higher quality crops, prolongation of house life, etc. Inthese large houses are used, as covering materials durable for about 5years, such covering materials as polyester resin panel, polycarbonateresin panel, hard vinyl chloride resin panel, acrylic resin panel,fiber-reinforced plastic panel and the like. Since these coveringmaterials have a large thickness, they have drawbacks in that they mustuse a specially made large base material and be spread, making theapplication very complicated and moreover they are relatively expensive.A polyester resin panel, a polycarbonate resin panel, a hard vinylchloride resin panel, an acrylic resin panel, etc. have further problemsin that they tend to generate cracks when hit by hail, etc. and thecracks tend to propagate.

Also, flat glass is used as a durable covering material which can beused for 10 years or more. Flat glass, however, has problems in that itis expensive and, moreover, it is broken easily and, once broken, thesoil inside house must be replaced to remove the fine pieces of brokenglass.

In order to solve these problems, Japanese Patent Application Kokai(Laid-Open) No. 43535/1989, for example, proposes an agriculturalcovering material comprising a fluororesin film.

While the above-mentioned conventional agricultural covering materialscontain a small amount of an ultraviolet absorber for improvement of theweatherability and generally have a property of intercepting theultraviolet rays of sunlight to some extent, a fluororesin film hasexcellent weatherability by itself and accordingly requires no use ofany weatherability improver (e.g. ultraviolet absorber) therein.Consequently, an agricultural covering material comprising a fluororesinfilm transmits even the ultraviolet rays of sunlight. Therefore, whenthe crop for in-house cultivation which had been subjected to breedingso as to fit the cultivation in a house covered with a conventionalagricultural covering material capable of intercepting ultraviolet raysto some extent, was cultivated in a house covered with a fluororesinfilm, there have arisen new problems not experienced with conventionalagricultural covering materials, such as delay of growth or harvestingtime, reduction in quality of harvest owing to, for example, thehardening of stem and leaf or of fruit, flower color darkening ordiscoloration of flowers and ornamental plants, and the like.

Fluororesin films are superior in mechanical strengths, transparency,weatherability, etc. and are best suited as a base material for use inan agricultural covering material which can be used in a spread stateover a long period of time, for example, 10 years or more. Hence, thepresent inventors made a study in order to solve the above-mentionedproblems possessed by an agricultural covering material comprising afluororesin film.

It is thought, as one mean for solving the problems, to use anultraviolet absorber in a fluororesin film as in the case ofconventional agricultural covering materials. However, fluororesins havea high melt-processing temperature and it is practically difficult touse therein an organic ultraviolet absorber such as used in conventionalagricultural covering materials.

The present inventors have developed a fluororesin film which can beused even for the conventional crops for in-house cultivation withoutinviting the above-mentioned problems, by using, in a fluororesin, aninorganic fine powder capable of withstanding the melt-processingtemperature of fluororesin.

DISCLOSURE OF THE INVENTION

According to the present invention there is provided an agriculturalcovering material comprising a fluororesin film which intercepts thetransmission of the ultraviolet rays having a wavelength range of atleast 300-330 nm, by at least 40% and which transmits at least 70% ofthe visible rays having a wavelength range of 400-800 nm.

The fluororesin film used as the agricultural covering material of thepresent invention intercepts the transmission of the portion of theultraviolet rays of sunlight, having a wavelength range of at least300-330 nm, by at least 40%, preferably 60% or more, more preferably 80%or more, most preferably 90% or more. The fluororesin film is notnecessarily required to intercept the transmission of the ultravioletrays having a wavelength longer than 330 nm, but it is desirable thatthe fluororesin film intercepts as well the transmission of theultraviolet rays having a wavelength range of about 350 nm or shorter byat least 40%, preferably 50% or more.

Meanwhile, the visible rays having a wavelength range of 400-800 nm,which are necessary for the growth of crops, are desired to betransmitted through the fluororesin film as much as possible. Thetransmittance of the visible rays through the fluororesin film is atleast 70%, preferably 80% or more, more preferably 85% or more, mostpreferably 88% or more. Herein, "the transmittance of the visible rayshaving a wavelength range of 400-800 nm" is an average transmittance ofthe visible rays in said wavelength range.

The fluororesin film having light transmission properties such asmentioned above can be produced, for example, by compounding, into afluororesin film, an inorganic powder capable of intercepting thetransmission of the ultraviolet rays having a wavelength range of atleast 300-330 nm, or by forming, on at least one side of a fluororesinfilm, a coating layer containing the above inorganic powder.

The fluororesin used as a base material in production of the above filmis a (co)polymer obtained from a fluorine-containing monomer(s).Specific examples thereof include a polytetrafluoroethylene (PTFE), atetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), atetrafluoroethylene-hexafluoropropylene copolymer (FEP), atetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinyl ethercopolymer (EPE), a tetrafluoroethylene-ethylene copolymer (ETFE), apolychlorotrifluoroethylene (PCTFE), a chlorotrifluoro-ethylene-ethylenecopolymer (ECTFE), a polyvinylidene fluoride (PVDF), a polyvinylfluoride (PVF), and a mixture of at least two of them. Of these, ETFE,PCTFE, ECTFE, PVDF and PVF are preferred; ETFE, PVDF and PVF are morepreferred; and ETFE is used particularly preferably.

ETFE is a copolymer of ethylene, tetrafluoroethylene (these twocomponents are major components and the molar ratio ofethylene/tetrafluoroethylene is generally 40/60 to 60/40) and, asnecessary, a small amount (generally 10 mole % or less) of a thirdcomonomer component. In the present invention, there is particularlypreferred an ethylene-tetrafluoroethylene type copolymer wherein themolar ratio of ethylene/tetrafluoroethylene is in the range of 40/60 to60/40, preferably 45/55 to 55/45 and wherein the content of aperfluoroalkylvinyl monomer unit represented by a formula CH₂ ═CH--C_(n)F_(2n+1) is an integer of 2-10) (for example, a unit derived from CH₂═CH--C₄ H₉ or CH₂ ═CH--C₆ H₁₃) is in the range of 0.1-10 mole %,preferably 0.3-5 mole %. This ethylene-tetrafluoroethylene typecopolymer is known per se; and it can be produced by, for example, aprocess described in Japanese Patent Publication No. 50163/1984, or itis commercially available under the brand name of "AFLON COP" (a productof Asahi Glass Co., Ltd.).

Meanwhile, the inorganic fine powder which can be compounded into thefluororesin, can be appropriately selected from oxides, compound oxides,sulfides, carbonates, etc. of metals such as titanium, zirconium,magnesium, calcium, barium, lanthanum, zinc, aluminum, tin, antimony,etc. Specific examples thereof include titanium oxide (TiO₂), zinc oxide(ZnO), mica, alumina (Al₂ O₃), colloidal silica (SiO₂), iron oxide (Fe₂O₃), cerium oxide (CeO₂), barium oxide (BaO), antimony oxide (Sb₂ O₃),nickel oxide (NiO), chromium oxide (Cr₂ O₃), zirconium oxide (ZrO₂),calcium oxide (CaO), tin oxide (SnO₂) and mixtures thereof. Of these,TiO₂, ZnO, CeO₂ and Fe₂ O₃ are preferred, and TiO₂ and ZnO areparticularly preferred.

The particle diameters of the inorganic fine powder are not particularlyrestricted as long as the fluororesin film can be endowed with theabove-mentioned optical properties. However, the average particlediameter of the inorganic fine powder is generally 1,000 nm or less,preferably 500 nm or less, more preferably 100 nm or less, particularlypreferably 50 nm or less.

The amount of the inorganic fine powder used in the fluororesin filmvaries depending upon the kind of the resin used and the thickness ofthe film used, but can be in the range of generally 0.01-10% by weight,preferably 0.1-5% by weight, more preferably 0.3-1% by weight.

The molding of a film from the fluororesin containing the inorganic finepowder can be conducted by a per se known method, for example, extrusionor inflation. The thickness of the film obtained can be generally10-1,000 μm, preferably 30-200 μm, particularly preferably 50-100 μm.

The fluororesin film having the above-mentioned light transmissionproperties can be produced also by coating, on the surface of aseparately produced fluororesin film having a thickness such asmentioned above, a coating fluid comprising an inorganic fine powdersuch as mentioned above and a resin binder.

In this case, it is desirable that the surface of the fluororesin filmis beforehand subjected to a surface-activating treatment in order toenable the uniform coating of the coating fluid on the surface of thefluororesin film, the tight adhesion of the formed coating layer to thefilm surface, and so forth.

The surface-activating treatment includes a corona discharge treatment,a sputtering etching treatment, a sodium treatment, a sandblastingtreatment, etc.

In the corona discharge treatment, discharge is allowed to take placebetween a knife edge electrode and an opposing electrode with a samplefilm placed between the electrodes; as a result, oxygen-containingfunctional groups such as aldehyde, acid, alcohol peroxide, ketone,ether and the like are formed on the film surface.

In the sodium treatment, the fluororesin film is immersed in a liquidammonia solution containing an alkali metal such as metallic sodium orthe like, whereby the CF₂ bond is allowed to disappear from the filmsurface and CH and C--O bonds are formed thereon.

In the sputtering etching treatment, a film sample is placed betweenelectrodes which are conducting glow discharge at a low pressure, toallow the positive ions generated by the glow discharge to hit the filmto form a large number of fine projections on the film.

In the sandblasting treatment, a sand of fine particles is blown againsta film to form a large number of fine roughnesses on the film surface.

Of these surface-activating treatments, the corona discharge treatmentis preferred in view of the adhesivity to the coating layer formed, theworkability, the safety, the cost, etc.

The resin binder usable in the coating fluid includes, for example, anacrylic resin, a vinyl acetate resin, a fluororesin and mixturesthereof. It is possible to optionally use, in combination with the resinbinder, a hydrophilic polymer, for example, a polyvinyl alcohol, apolyvinylpyrrolidone or a polymer generally having a hydrophilicfunctional group such as --SO₄, --SO₃ H, --COOH, --CN, --(OCH₂ CH₂) orthe like.

The coating fluid may further contain, as necessary, a surfactant suchas sorbitan-fatty acid ester, sorbitol-fatty acid ester,diglycerine-fatty acid ester, glycerine-fatty acid ester, sorbitan-fattyacid-dibasic acid ester, sorbitol-fatty acid-dibasic acid ester,diglycerine-fatty acid-dibasic acid ester, glycerine-fatty acid-dibasicacid ester and addition compound obtained by adding an alkylene oxide(e.g. ethylene oxide or propylene oxide) to any of the above esters.

The above-mentioned components are dissolved or dispersed in, forexample, water or a solvent of alcohol, ketone, ester or ether type toprepare a coating fluid, and the coating fluid is coated on thefluororesin film. The coating can be conducted by an ordinary methodsuch as brush coating, dip coating, gravure coating, spray coating orthe like.

In the coating fluid, the concentration of the inorganic fine powdervaries depending upon the thickness of the coating fluid coated, thekind of the resin binder used, etc. However, the content of theinorganic fine powder in the coating layer formed is desirably in therange of generally 0.5-95% by weight, preferably 1-50% by weight, morepreferably 3-30% by weight.

The thickness of the coating layer formed is not strictly restricted aslong as the resulting film has the above-mentioned light transmissionproperties, but can be in the range of generally 1-100 μm, preferably2-50 μm, more preferably 5-20 μm.

The fluororesin film, which can be produced as mentioned above and whichhas the above-mentioned light transmission properties, showssubstantially no change in properties even when used outdoors as anagricultural covering material in a spread state over a long period oftime such as 10 years or more, and can be applied to various crops whichhave been subjected to breeding for in-house cultivation, withoutcausing the above-mentioned problems. Therefore, the fluororesin filmcan be widely used as a covering material for green house, to replaceglass.

According to the present invention, there is also provided a method forcultivation of useful crops, which comprises cultivating useful crops ina greenhouse covered with an agricultural covering material comprisingthe above-mentioned fluororesin film.

Herein, "useful crops" include agriculture, horticulture and forestrycrops useful in human life, and are exemplified by the followings.

1! Agriculture and horticulture crops

(1) Food crops

Rice, wheat, corn, soybean, sweet potato, potato

(2) Garden crops

Fruit trees

Apple, pear, persimmon, peach, Japanese apricot, grape, loquat, fig,blueberry, pomegranate, lemon, oranges, etc.

Fruit vegetables

Cucumber, watermelon, tomato, strawberry, pumpkin, melon, eggplant, pea,okura, pimento

Root vegetables

Carrot, burdock, taro, ginger, lotus root, wasabi (Japanesehorseradish), arrow head, scallion

Leaf vegetables

Chinese cabbage, white stemmed onion, garlic, onion, cabbage, Japaneseparsley, spinach, beefsteak plant, Japanese butterbur, celery, gynmight,parsley, trefoil, asparagus, udo salad plant

Flowers (annual and biennial)

Morning glory, cosmos, Iceland poppy aster, yellow sultan, snapdragon,calendura, stock, pansy, sunflower, benidium, dimolphoseca, safflower,white lace flower, cornflower, prairie gentian, lodans

Perenial plants

Lawn grasses, oriental orchid, gypsophila, carnation, gerbera,bellflower, chrysanthemum, rabbit-ear-iris, statice, peony, marguerite

Bulbous plants

Lilies, gladiolus, iris, anemone, calla, daffodil, freesia, ranunculus,blackberry lily

Flowering trees and shrubs

Acasia, azelea, rose, mewsyran, lagerstroemia, winter daphne,chloranthus glaber MAKINO, cyad (Japanese sago palm), camellia, tea oilplant, encalyptus

Greenhouse plants

Orchid, cyclamen

(3) Industrial crops

Oil crops

Rapeseed, sesame

Sugar crops

Sugar cane, sugar beet

Fiber crops

Cotton, hemp, flax, jute

Starch crops

Konjac

Medical herbs

Japanese peppermint, poppy

Recreation crops

Tea, tobacco, hop

Paper-making crops

Paper mulberry, mitsumata

Dye crops

Japanese indigo plant

Flavoring crops

Geranium

Sap crops

Lacquer tree

(4) Forage crops

Forage crops

Orchard grass, red clover, white clover

Plants for feed and manure

Bread tree, silk tree

Green manure crops

Chinese milk vetch, bur clover

2! Forestry trees

Coniferous trees

Japanese cedar, Japanese cypress, pine tree

Broad leaved evergreens

Aucuba, fatsia

Broad leaved deciduous trees

Nara oak, Siebold's beech

Of these crops, those to which the agricultural covering material of thepresent invention is applicable particularly favorably, are gardencrops; preferably fruit vegetables, root vegetables, leaf vegetables,flowers, perennial plants, flowering trees and shrubs, and greenhouseplants; more preferably fruit vegetables, flowers, perennial plants, andflowering tress and shrubs; most preferably fruit vegetables, andflowering trees and shrubs.

The fruit vegetables to which the present agricultural covering materialis applicable favorably, include cucumber, watermelon, tomato,strawberry, melon and pimento, with cucumber, melon and tomato beingparticularly preferred; the root vegetables are preferably carrot andginger; and the leaf vegetables are preferably Chinese cabbage, whitestemmed onion, celery and trefoil.

The flowers to which the present agricultural covering material isapplicable favorably, include stock and prairie gentian; the perennialplants include oriental orchid, gypsophila, carnation, gerbera,chrysanthemum and statice with carnation, gerbera and chrysanthemumbeing particularly preferred; the bulbous plants are preferably liliesand iris; and the flowering trees and shrubs are preferably rose.

By cultivating these useful crops in a green-house covered with theagricultural covering material of the present invention, there can beobtained various cultivation effects which have not been obtainable withconventional agricultural covering materials, as shown in Examplesdescribed later. The effects are summarized as follows.

(1) When the agricultural covering material of the present invention isused, as compared with when conventional covering materials are used,cultivation is very easy. Therefore, farmers do not fail in cultivationand can obtain a stable yield.

(2) When the agricultural covering material of the present invention isused, as compared with when conventional covering materials are used, aharvest of good quality can be obtained in a large amount, and a highprofit is promised.

Examples

The present invention is hereinafter described more specifically by wayof Examples.

Examples of production of films

Production Example A (a comparative example)

Into an autoclave having an internal volume of 10 liters were fed 3.46kg of trichloromonofluoromethane, 6.52 kg of trichlorotrifluoroethaneand 2.38 g of t-butyl peroxyisobutyrate. Thereto were fed 1,226 g oftetrafluoroethylene, 82 g of ethylene and 26 g of perfluorobutylethylene(CH₂ ═CH--C₄ F₉). The resulting mixture was subjected to acopolymerization reaction with sufficient stirring with the reactiontemperature being kept at 65° C.

During the copolymerization reaction, the polymerization pressure waskept at 15.0 kg/cm² by introducing into the system atetrafluoroethylene/ethylene/perfluorobutylethylene (molar ratio:53/46.3/0.7) mixed gas. After 5 hours, 460 g of a white copolymer(hereinafter referred to as resin No. 1) was obtained. The copolymer hada C₂ F₄ /C₂ H₄ /CH₂ ═CHC₄ F₉ molar ratio of 53/46.3/0.7, a flow-startingtemperature of 267° C. and a pyrolysis-starting temperature of 360° C.

The above-obtained ethylene-tetrafluoroethylene type copolymer(hereinafter abbreviated to "ETFE" in some cases) was extruded at aresin temperature of 320° C. to produce a film No. 1 having a thicknessof 60 μm.

Production Example B (a comparative example)

There were mixed 67 parts by weight of a polyvinyl chloride(polymerization degree: 1,300), 25 parts by weight of dioctyl phthalate(a plasticizer), 5 parts by weight of tricresyl phosphate (aplasticizer), 3 parts by weight of an epoxidized soybean oil (aplasticizer), 0.8 part by weight of barium licinolate (a stabilizer),0.5 part by weight of zinc stearate (a stabilizer), 0.3 part by weightof dibutyltin maleate (a stabilizer), 0.6 part by weight of sorbitanmonopalmitate (a surfactant) and 5 parts by weight of2-hydroxy-4'-methoxybenzophenone (an ultraviolet absorber). Theresulting mixture was melt-extruded at 200° C. by the use of an extruderto obtain a film No. 4 having a thickness of 60 μm.

Production Example C (present invention)

A film No. 2 having a thickness of 60 μm was obtained in the same manneras in Production Example A except that 0.2% by weight of zinc oxide(ZnO) having an average particle diameter of 20 nm was added to the EFTEobtained in Production Example A.

Production Example D (present invention)

One side of the film No. 1 obtained in Production Example A wassubjected to a corona discharge treatment under the conditions ofdischarge current=10A, discharge voltage=120 V and line speed=13 m/min.Separately, 5% by weight of a polyvinyl alcohol and 5% by weight of TiO₂having an average particle diameter of 30 nm were added to a silica sol(solid silica content=8%), and the mixture was diluted 100-fold withethanol to prepare a coating fluid. The coating fluid was coated on theabove-treated side of the film No. 1 in an amount of 15 g/m² to obtain afilm No. 3.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the curves of light transmittances at various wavelengths,of the film Nos. 1-4 obtained in the above Production Examples A-D.

Evaluations of film properties

1. Transparency

There were prepared, as conventional agricultural covering materials, asoft vinyl chloride resin film Noubi Ace (trade name), a product ofMitsubishi Chemical MKV Co., 100 μm!, a poly ester film SIKUSURAITO(trade name), a product of Taiyo Kogyo Co., Ltd., 175 μm!, apolycarbonate resin panel Iupilon (trade name), a product of MitsubishiGas Chemical Co., Inc., 1,000 μm! and an acrylic resin panel Acryl Panel(phonetical translation) (trade name), a product of Mitsubishi RayonCo., Ltd., 1,700 μm!. These conventional covering materials and the filmNos. 1-4 obtained in the above Production Examples were fixed on anoutdoor exposure stand having an inclination of 45° and looking towardthe south, located at Uozu City, Toyama Prefecture, Japan.

After 4 years of outdoor exposure, all the agricultural coveringmaterials were recovered and measured for average light transmittance ofvisible rays having a wavelength range of 400-800 nm, by the use of aspectrophotometer. The results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                           Light transmittance (%)                                                   Thickness Before    After                                      Agricultural covering material                                                               (μm)   exposure  exposure                                   ______________________________________                                        Film No. 2     60        91        85                                         Film No. 3     62        93        87                                         Film No. 1     60        93        87                                         Film No. 4     60        88        15                                         Soft vinyl chloride resin film                                                               100       87        21                                         Polyester film 175       90        50                                         Polycarbonate resin panel                                                                    1,000     88        48                                         Acrylic resin panel                                                                          1,700     94        45                                         ______________________________________                                    

As is clear from Table 1, each of the soft vinyl chloride resin film,the polyester film, the polycarbonate resin panel, the acrylic resinpanel (these are conventional covering materials), and the film No. 4containing a large amount of an ultraviolet absorber gave 50% or less ofa light transmittance after 4 years of outdoor exposure and becameunusable as an agricultural covering material.

In contrast, the film Nos. 1-3 each comprising a fluororesin showedsubstantially no reduction in tansparency after outdoor exposure andkept substantially the same transparency a s before exposure.

2. Impact resistance

In order to evaluate the impact resistance of a sample film when hit bythe wood pieces carried by a typhoon, a small stone having a weight of300 g was dropped, from a height of 50 cm, on each of the film Nos. 2-3and also on a flat glass (a product of Asahi Glass Co., Ltd., thickness:3 mm) to examine the extent of the damage.

As a result, the flat glass was broken into fine pieces while the filmNos. 2-3 were not broken and had no damage.

From the above, it is presumed that a flat glass is easily broken by,for example, hail or the objects carried by typhoon and consequently theuseful crops cultivated in a greenhouse covered with a flat glassreceive deadly damage.

It was found out from the above tests that, of conventional agriculturalcovering materials, those satisfactory in transparency and impactresistance are only fluororesin films.

Examples of cultivation of useful crops

1! Evaluation of cultivation of tomato

Each of the film Nos. 1-4 obtained in Examples of production of filmswas spread on a house (width: 10 m, depth: 20 m).

(1) Cultivation-1

Tomato seeds (variety: momotaro) were sown on August 25 to raiseseedlings. On October 2, young seedlings in uniform growth in which 2-3first clusters were in bloom, were set in each house so as to give anintrarow spacing of 50 cm.

The amounts of applied fertilizers are shown in Table 2. For about 10days after setting, watering was made in a relatively small amount insuch an extent that the young seedlings showed no wilting and made norapid growth. The temperature of cultivation was controlled at 28° C. inthe morning, at 25° C. in the afternoon and at 5° C. or higher duringthe night. Therefore, hot-air heating was conducted with a heater duringlow-temperature seasons.

                  TABLE 2                                                         ______________________________________                                                  Amount of                                                                            Fertilizer                                                             fertilizer                                                                           components                                                             applied                                                                              (Kg/10 a)                                                    Name of fertilizer                                                                        (Kg/10 a)                                                                              N      P    K    Remarks                                 ______________________________________                                        Compound fertilizer                                                                       200      16     --   --   Initial manure                          for exclusive use in                                                          tomato                                                                        Magnesium-containing                                                                      30       --     10.5 --   Initial manure                          calcined phosphate                                                            Fused phosphate                                                                           40       --     8    --   Initial manure                          fertilizer                                                                    Potassium sulfate                                                                         30       --     --   15   Initial manure                          Sumika Ace  150      22.5   15   21   Additional                                                                    manure                                  E No.2 (liquid                                                                            75       6      3    4.5  Additional                              fertilizer)                           manure                                  ______________________________________                                    

Harvesting was conducted from December 10 through May 30, next year. Theresults of yield and other inspections are shown in Table 3.

The inspection items and the evaluation methods therefor are shownbelow.

Yield: an index when the total weight of the harvest obtained in thehouse covered with the film No. 4 was taken as 100.

The same calculation was made also in other cultivation examples.

                  TABLE 3                                                         ______________________________________                                                               Compara- Compara-                                                             tive     tive                                                                 Cultiva- Cultiva-                                               Cultiva-                                                                            Cultiva-                                                                              tion     tion                                                   tion Ex-                                                                            tion Ex-                                                                              Example  Example                                                                              Re-                                             ample 1                                                                             ample 2 1        2      marks                                  ______________________________________                                        No. of spread film                                                                        2       3       1      4                                          1.  Yield      121     135   108    100                                       2.  Quality                                                                       (1) Hardness of                                                                          Ade-    Ade-  Hard   Soft                                          exodermis  quate   quate                                                      (2) Color of                                                                             Pink    Bright                                                                              Dark red                                                                             Light                                         exodermis          pink         pink                                          (3) Color of                                                                             Pink    Pink  Orange Light  Jelly                                  fruit inside             with re-                                                                             pink   portion                                                         maining                                                                       dark                                                                          green                                            3.  Outbreak of                                                                   diseases                                                                      (1) Frequency                                                                            Low     Low   Low    High   Gray                                   of outbreak                            mold                                   (2) Infectivity                                                                          Weak    Weak  Strong Weak                                          of diseases                                                               4.  Vermination                                                                              Small   None  Large  None   Green-                                 of injurious                                                                             amount        amount        house                                  insects                                whitefly                           ______________________________________                                    

In the house covered with the film No. 1, the growth of tomato was slow;the stem and leaf and the fruit were hard; and the plant was small as awhole. Consequently, the timing of harvesting was later than in thehouses covered with other films. Moreover, the balance between the colorof the exodermis of fruit and the color of jelly portion inside fruitwas not normal, and the color inside fruit was still green (unripe) butthe color of exodermis was already ripe.

In the house covered with the film No. 4, the house inside became highlyhumid and the growth of the plant was too active, resulting in lowyield. Moreover, the plant was soft as a whole and the colors of stemand leaf and fruit were light; this is presumed to be the reason for thehigh frequency of the outbreak of diseases.

(2) Cultivation-2

The cultivation management for next year was changed as follows based onthe results of Cultivation-1, and cultivation (Cultivation-2) wasconducted.

In the houses covered with the film Nos. 2-3, the same cultivationconditions as in Cultivation-1 were used.

In the house covered with the film No. 1, the amount of each fertilizerapplied was increased by 10%; the total amount of water applied wasincreased by 10-15%; the night temperature was kept higher by 1° C.;whenever direct sunlight was intense, a black cheese cloth capable ofintercepting the light by 50% was spread at the ceiling.

In the house covered with the film No. 4, the amount of each fertilizerapplied was decreased by 15%; the amount of water applied was decreasedby about 20%; the night temperature was set lower by 1° C.; and leafpicking was as necessary made so that the plant could receive sunlightas much as possible.

Thus, in the houses covered with the film No. 1 and 4, the time spent byfarmer for operation was about 1.5-2 times those spent in the cases ofthe film Nos. 2-3. Particularly in the house covered with the film No.1, the intensity of sunlight had to be checked as necessary, whichdisturbed other agricultural works. The results of cultivation are shownin Table 4.

                  TABLE 4                                                         ______________________________________                                                                   Compara- Compara-                                                             tive     tive                                                 Cultiva-                                                                             Cultiva- Cultiva- Cultiva-                                             tion   tion     tion     tion                                                 Example 3                                                                            Example 4                                                                              Example 3                                                                              Example 4                                 ______________________________________                                        No. of spread film                                                                          2        3        1      4                                      1.  Yield        104      120    102    100                                   2.  Quality                                                                       (1) Hardness of                                                                            Adequate Adequate                                                                             Slightly                                                                             Slightly                                  exodermis                    hard   soft                                      (2) Color of Pink     Bright Red    Light pink                                exodermis             pink                                                    (3) Color of fruit                                                                         Pink     Pink   Dark red                                                                             Light pink                                inside                                                                    ______________________________________                                    

As is clear from Table 4, in each of the houses covered with the filmNos. 1 and 4, the yield increased over the previous year and was aboutequal to that when the film No. 2 was used, but was lower than that whenthe film No. 3 was used. The plant qualities when the film No. 1 and 4were used, were inferior to those when the film Nos. 2 and 3 were used.

As seen from the above results of 2-year cultivation, when the film Nos.2-3 were used, cultivation of tomato was very easy as compared with whenthe conventional film Nos. 1 and 4 were used; there was no failure incultivation; and a stable yield could be obtained.

Further, the harvested tomato had excellent quality, giving a very highprofit.

2! Example of cultivation of cucumber

Cucumber seeds (variety: Sharp One) were sown on September 15 to raiseseedlings. The seedlings were grafted to a stock (variety: King Tosa) onSeptember 22. The grafted seedlings were raised so as to give uniformgrowth. On October 19, the young seedlings having 3.5 true leaves wereset in each of the houses (width: 10 m, depth: 20 m) covered with thefilm Nos. 1-4, in a density of 4.8 plants/tsubo (3.3 m²).

The amount of each fertilizer applied is shown in Table 5. Until thenumber of nodes became 13-15, watering was kept as low as possible andthe in-house temperature was controlled not to reach 25° C. or higher.Thereafter, care was taken in order for the in-house minimum temperaturenot to become 11° C. or lower.

                  TABLE 5                                                         ______________________________________                                                         Amount of                                                                     fertilizer                                                                    applied                                                      Name of fertilizer                                                                             (kg/10 a) Remarks                                            ______________________________________                                        Compound fertilizer for cucumber                                                               600       Initial manure                                     Fermented chicken droppings                                                                    600       Initial manure                                     Magnesium lime   80        Initial manure                                     Rice straw compost                                                                             2,000     Initial manure                                     E No. 2 (liquid fertilizer)                                                                    100       Additional manure                                  OKF-2            100       Additional manure                                  ______________________________________                                    

Harvesting was conducted from November 20 through May 10, next year. Theresults of cultivation are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                               Compara- Compara-                                                             tive     tive                                                                 Cultiva- Cultiva-                                               Cultiva-                                                                            Cultiva-                                                                              tion     tion                                                   tion Ex-                                                                            tion Ex-                                                                              Example  Example                                                                              Re-                                             ample 5                                                                             ample 6 5        6      marks                                  ______________________________________                                        No. of spread film                                                                        2       3       1      4                                          1.  Yield      125     133   98     100                                       2.  Quality                                                                       Color of fruit                                                                           Green   Bright                                                                              Dark   Light                                                    green   green green                                                Hardness of                                                                              Ade-    Ade-  Hard   Soft                                          fruit      quate   quate                                                  3.  Condition of                                                                  leaves                                                                        Color      Green   Bright                                                                              Dark   Light                                                            green green  green                                         Sunscald   None    None  Seen   None                                          Aging      None    None  Seen   None                                      4.  Outbreak of                            Gray                                   diseases                               mold                                   Frequency of                                                                             Low     Low   Low    High                                          outbreak                                                                      Infectivity of                                                                           Weak    Weak  Strong Weak                                          diseases                                                                  5.  Vermination of                                                                           Small   None  Large  None   Green-                                 injurious  amount  amount              house                                  insects                                white-                                                                        fly,                                                                          aphid                              ______________________________________                                    

As is clear from Table 6, in the house covered with the film No. 1,cucumber grew hard; the aging of leaves (that is, the leaves showedsunscald and reduced luster, then became blackish, and finally withered)was earlier by about 15-20 days than in the houses covered with otherfilms; the plant vigour was weak; the growth was slower; and the timingof harvesting was later than in other houses.

In the house covered with the film No. 4, the humidity was higher thanin the houses covered with other films and was incessantly high. Partlyowing to this fact, the plant vigour was strong; the plant was weak as awhole; the growth was active; and the yield of fruit was not large.

Presumably owing to the weakness of whole plant, the damage by diseases,particularly the damage by gray mold was large.

In contrast, in the houses covered with the film Nos. 2-3, cultivationwas possible with substantially no extra labor required; the yield waslarge; the plant quality was good; and the profitability was very high.

In the houses covered with the film Nos. 1 and 4, there were newlyemployed the same fertilizer amount, watering amount, temperaturecontrol and sunlight control as in the second year of tomatocultivation. As a result, the yields increased to about the same levelas in the house covered with the film No. 2.

3! Example of cultivation of melon

Melon seeds (variety: Andes) were sown on January 15 to raise seedlings.On February 10, the seedling having 2 true leaves were set in each ofthe houses shown in Table 7, in a density of 1,500 plants/tan (991 m²).Emerald sem was used as a stock and grafting was conducted by inarching.

Harvesting was conducted from May 20 through June 15. The results ofcultivation are shown in Table 7.

The melons harvested in the houses covered with the film Nos. 2-3, ascompared with those harvested in the houses covered with the film Nos. 1and 4, gave higher yields and higher qualities, could be marketed ashigh-quality products, and gave higher profitabilities.

                  TABLE 7                                                         ______________________________________                                                               Compara- Compara-                                                             tive     tive                                                                 Cultiva- Cultiva-                                               Cultiva-                                                                            Cultiva-                                                                              tion     tion                                                   tion Ex-                                                                            tion Ex-                                                                              Example  Example                                                                              Re-                                             ample 7                                                                             ample 8 7        8      marks                                  ______________________________________                                        No. of spread film                                                                       2       3       1      4                                           1.  Condition of                                                                  leaves                                                                        (1) Color  Green   Bright                                                                              Dark   Light                                                            green green  green                                         (2) Sunscald                                                                             None    None  Seen   None                                      2.  Yield      116     121   103    100                                       3.  Quality                                                                       (1) Saccharose                                                                           13.9    14.1  13.3   13.5                                          content                                                                       (2) Condition                                                                            Good    Good  Good   Coarse                                        of net                                                                    4.  Outbreak of                            Gray                                   diseases                               mold                                   (1) Frequency                                                                            Low     Low   Low    High                                          of outbreak                                                                   (2) Infectivity                                                                          Weak    Weak  Strong Weak                                          of diseases                                                               5.  Vermination of                                                                           Small   None  Large  None   Green-                                 injurious  amount        amount        house                                  insects                                white-                                                                        fly,                                                                          aphid                              ______________________________________                                    

4! Example of cultivation of pimento

Pimento seeds (variety: Shin Sakigake No. 2) were sown on July 30 toraise seedlings. The seedlings were subjected to "kuntan" culture andset in each house on August 30 in a density of 3.7 plants/tsubo (3.3m²), and cultivation was continued. When the plant height became about25 cm, four primary scaffold branches were erected and each connected toa plastic string hanged down from the top of the house. In this state,cultivation was further continued.

Harvesting was conducted from November 15 through May end, next year.The results of cultivation are shown in Table 8.

                  TABLE 8                                                         ______________________________________                                                               Compara- Compara-                                                             tive     tive                                                                 Cultiva- Cultiva-                                              Cultiva-                                                                            Cultiva- tion     tion                                                  tion Ex-                                                                            tion Ex- Example  Example                                                                              Re-                                            ample 9                                                                             ample 10 9        10     marks                                  ______________________________________                                        No. of spread                                                                           2       3        1      4                                           film                                                                          1.  Yield     123     135    110    100                                       2.  Vermination                                                                             Small   None   Large  None   Yellow                                 of injurious                                                                            amount         amount        thrip                                  insects                                                                   ______________________________________                                    

5! Example of cultivation of watermelon

Watermelon seeds (variety: Shimao Max KE) were sown on December 25 toraise seedlings. On January 13, next year, the young seedlings weregrafted to gourd (a stock) by cutting grafting. On February 10, thegrafted seedlings were set in the balks (balk-to-balk distance: 2 m) ofeach of the houses shown in Table 9, in a density of 520 plants/tan (991m²), and cultivation was continued. Harvesting was conducted from April25 through June mid. The results of cultivation are shown in Table 9.

                  TABLE 9                                                         ______________________________________                                                               Compara- Compara-                                                             tive     tive                                                   Cultiva-                                                                            Cultiva-                                                                              Cultiva- Cultiva-                                               tion Ex-                                                                            tion Ex-                                                                              tion     tion                                                   ample ample   Example  Example                                                                              Re-                                             11    12      11       12     marks                                  ______________________________________                                        No. of spread film                                                                       2       3       1      4                                           1.  Yield      118     125   98     100                                       2.  Quality                                                                       Saccharose 11.6    11.8  11.3   10.9                                          content                                                                   3.  Outbreak of                            Gray                                   diseases                               mold,                                                                         sclero-                                                                       fal                                                                           disease                                (1) Frequency                                                                            Low     Low   High   Low                                           of outbreak                                                                   (2) Infectivity                                                                          Weak    Weak  Strong Weak                                          of diseases                                                               4.  Vermination                                                                              Small   Small Large  Small  aphid                                  of injurious                                                                             amount  amount                                                                              amount amount                                        insects                                                                   ______________________________________                                    

6! Examples of cultivation of celery and carrot

Celery seeds (variety: Cornel 619) were sown on December 1 to raiseseedlings. On March 30, the seedlings were set in each of the housesshown in Table 10. Harvesting was conducted for 10 days starting fromJune 20. The results of cultivation are shown in Table 10.

On January 31, carrot seeds (variety: Kosei gosun) were sown in each ofthe houses shown in Table 11, to raise seedlings. On February 20, theseedlings of delayed growth were removed for thinning so as to give anintrarow spacing of 20 cm, and cultivation was continued. Harvesting wasconducted from May 10 through May 15. The results of cultivation areshown in Table 11.

                  TABLE 10                                                        ______________________________________                                                               Compara- Compara-                                                             tive     tive                                                   Cultiva-                                                                            Cultiva-                                                                              Cultiva- Cultiva-                                               tion Ex-                                                                            tion Ex-                                                                              tion     tion                                                   ample ample   Example  Example                                                                              Re-                                             13    14      13       14     marks                                  ______________________________________                                        No. of spread film                                                                       2       3       1      4                                           1.  Yield      118     122   81     100                                       2.  Quality                                                                       (1) Color of                                                                             Green   Bright                                                                              Excess-                                                                              Light                                         whole plant        green ively  green                                                                  dark                                                                          green                                                (2) Hardness of                                                                          Ade-    Ade-  Too hard                                                                             Soft                                          whole plant                                                                              quate   quate                                                  3.  Outbreak of                            Mainly                                 diseases                               sclero-                                                                       fal                                                                           disease                                (1) Frequency                                                                            Low     None  High   High                                          of outbreak                                                                   (2) Infectivity                                                                          Weak    --    Strong Weak                                          of diseases                                                               ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                                               Comparative                                                          Cultivation                                                                            Cultivation                                                          Example 15                                                                             Example 15                                             ______________________________________                                        No. of spread film                                                                            3          4                                                  1.     Yield        124        100                                            2.     Quality                                                                       (1) Color    Bright crimson                                                                           Crimson                                        ______________________________________                                    

7! Example of cultivation of rose

On December 20, rose seedlings (variety: Curl Red) were set in the house(width: 20 m, depth: 50 m) covered with the film No. 1 so as to give anintrarow spacing of 40 cm, and cultivation was conducted with thein-house temperature being kept at 16° C. or higher. Harvesting wasconducted from May 30 to November 30. The results of cultivation areshown in Table 12.

In Table 12, yield refers to an index when the total number of the rosesharvested in the house covered with the film No. 4 was taken as 100.

                  TABLE 12                                                        ______________________________________                                                              Compara- Compara-                                                                             Compara-                                                      tive     tive   tive                                            Cultiva-                                                                            Cultiva-                                                                              Cultiva- Cultiva-                                                                             Cultiva-                                        tion Ex-                                                                            tion Ex-                                                                              tion     tion   tion                                            ample ample   Example  Example                                                                              Example                                         16    17      16       17     18                                      ______________________________________                                        No. of spread                                                                            2       3       1      4      1                                    film                                                                          1.  Sunscald of                                                                             Slight  None  Much   A little                                                                             Slight                                  leaves                                                                    2.  Yield (num-                                                                             128     134   92     100    115                                     ber of har-                                                                   vested roses)                                                             3.  Quality                                                                       (1) Flower                                                                              Crim-   Bright                                                                              Blackened                                                                            Light  Slightly                                color (petal)                                                                           son     crimson                                                                             (striped)                                                                            color  blackened                                                              (faint                                                                        color)                                     4.  Outbreak of                                                                   diseases                                                                      (gray mold)                                                                   (1) Frequen-                                                                            None    None  Low    High   Low                                     cy of out-                                                                    break                                                                         (2) Infectiv-                                                                           --      --    Strong Weak   Strong                                  ity of                                                                        diseases                                                                  5.  Vermination                                                                             Small   None  Large  Large  None                                    of injurious                                                                            amount        amount amount                                         insects                                                                       (aphid)                                                                   Frequent use of                                                                         No      No      No     No     Yes                                   of cheese cloth                                                               ______________________________________                                    

As is clear from Table 12, the roses cultivated in the house coveredwith the film No. 1 generated a large number of black striped stains inthe petals and were not marketable.

To prevent the above phenomenon, a black cheese cloth capable ofintercepting 50% of sunlight was spread at the ceiling of the housewhenever sunlight was intense, whereby no intense sunlight was allowedto directly hit the roses. As a result, the amount of the black stainsgenerated was reduced to about 1/3. Meanwhile, when the cheese cloth wasspread more frequently to decrease the amount of sunlight applied, theflower color of rose became light, causing a faint color phenomenon andgiving lower quality.

In the house covered with the film No. 4, the flower color of rosebecame light and the roses harvested had a problem in commercial value.The high humidity in the house is presumed to have been one reason forthe light flower color. It is presumed that, in a high humidity, thetree became soft and came to have reduced disease resistance and reducedinjurious insect resistance. For prevention thereof, an agriculturalchemical was spread, which gave stains owing to the agriculturalchemical and an even lower commercial value.

In contrast, in the houses covered with the film Nos. 2-3, the flowercolor of rose was very bright crimson. Particularly, the rosescultivated in the house covered with the film No. 3 had a highcommercial value.

As seen above, in the houses covered with the film Nos. 2-3, as comparedwith in the houses covered with the film Nos. 1 and 4, cultivation wasvery easy; there was no failure in cultivation by farmer and a stableyield was possible; moreover, high quality rose could be produced in alarge amount; consequently, a high profit could be obtained.

8! Examples of cultivation of prairie gentian and gerbera

Prairie gentian seeds (variety: Domino Pastel) were sown on July 20 toraise seedlings. On September 30, the young seedlings were set in eachhouse, and cultivation was continued. Harvesting was conducted fromJanuary 15 through March 5.

The results of cultivation are shown in Table 13.

In Table 13, yield refers to an index when the total number of theprairie gentian harvested in the house covered with the film No. 4 wastaken as 100.

                  TABLE 13                                                        ______________________________________                                                              Compara- Compara-                                                                             Compara-                                                      tive     tive   tive                                            Cultiva-                                                                            Cultiva-                                                                              Cultiva- Cultiva-                                                                             Cultiva-                                        tion Ex-                                                                            tion Ex-                                                                              tion     tion   tion                                            ample ample   Example  Example                                                                              Example                                         18    19      19       20     21                                      ______________________________________                                        No. of spread                                                                            2       3       1      4      1                                    film                                                                          1.  Yield (num-                                                                             124     135   89     100    118                                     ber of harv-                                                                  ested plants)                                                             2.  Quality                                                                       (1) Flower                                                                              Crim-   Bright                                                                              Blackened                                                                            Light  Light                                   color     son     crimson                                                                             (striped)                                                                            color  crimson                             Frequent use of                                                                         No      No      No     No     Yes                                   cheese cloth                                                                  ______________________________________                                    

As is clear from Table 13, in the house covered with the film No. 1, theprairie gentian generated a large number of black stains in the petalsand could not be marketable.

For prevention thereof, the same cheese cloth as used in ComparativeCultivation Example 18 was used in the same manner as in ComparativeCultivation Example 18. As a result, frequent use of cheese cloth coulddiminish the black stains as in the flower of rose, but the flower colorbecame light and the flower quality dropped.

In the house covered with the film No. 4, the flower color became light,posing a problem in commercial value.

In contrast, in the houses covered with the film Nos. 2 and 3, a largenumber of prairie gentian having a bright flower color could beharvested.

Results of cltivation similar to those of prairie gentian were obtainedalso in cultivation of gerbera (variety: Smoke World).

What is claimed is:
 1. An agricultural covering material comprising afluororesin film which intercepts a transmission of ultraviolet rayshaving a wavelength range of at least 300-330 nm, by at least 40% andwhich transmits at least 70% of visible rays having a wavelength rangeof 400-800 nm, wherein the fluororesin film comprises an inorganic finepowder capable of intercepting the transmission of the ultraviolet rayshaving the wavelength range of at least 300-330 nm.
 2. An agriculturalcovering material according to claim 1, wherein the fluororesin filmhas, on at least one side thereof, a coating layer containing inorganicfine powder capable of intercepting the transmission of the ultravioletrays having a wavelength range of at least 300-330 nm.
 3. Anagricultural covering material according to claim 1 or 2, wherein theinorganic fine powder is titanium oxide, zinc oxide or a mixturethereof.
 4. An agricultural covering material according to claim 1,wherein the film contains 0.01-10% by weight of said inorganic finepowder.
 5. An agricultural covering material according to claim 2,wherein the coating layer contains 0.5-95% by weight of said inorganicfine powder.
 6. An agricultural covering material according to claim 1,wherein the fluororesin film is an ethylene/tetra-fluoroethylenecopolymer obtained by copolymerizing ethylene, tetrafluoroethylene and,as necessary, 10 mole % or less of a C₄ -C₁₂ perfluoroalkylvinylmonomer, the molar ratio of ethylene and tetrafluoroethylene being inthe range of 40/60 to 60/40.
 7. A greenhouse covered with theagricultural covering material of claim
 1. 8. A method for thecultivation of useful crops, which comprises cultivating said usefulcrops in a greenhouse covered with the agricultural covering material ofclaim
 1. 9. An agricultural covering material comprising a fluororesinfilm which intercepts a transmission of ultraviolet rays having awavelength range of at least 300-330 nm, by at least 40% and whichtransmits at least 70% of visible rays having a wavelength range of400-800 nm,wherein the fluororesin film is 30-200 μm thick and comprisesan ethylene/tetrafluoroethylene copolymer obtained by copolymerizingethylene, tetrafluoroethylene and 0 to 10 mole % of a C₄ -C₁₂perfluoroalkylvinyl monomer, the molar ratio of ethylene andtetrafluoroethylene being in the range of 40/60 to 60/40 and aninorganic fine powder having a particle size of 20 to 500 nm capable ofintercepting the transmission of the ultraviolet rays having thewavelength range of at least 300-330 nm.
 10. An agricultural coveringmaterial according to claim 9, wherein the film contains 0.1 to 5% byweight of said inorganic fine powder.
 11. An agricultural coveringmaterial according to claim 9, wherein the fluororesin film has, on atleast one side thereof, a coating layer 2 to 50 μm thick containing 1 to50% by weight of said inorganic fine powder capable of intercepting thetransmission of the ultraviolet rays having a wavelength range of atleast 300-330 nm.
 12. An agricultural covering material according toclaims 9, 10 or 11, wherein the inorganic fine powder is a memberselected from the group consisting of titanium oxide, zinc oxide andmixtures thereof.
 13. A greenhouse covered with the agriculturalcovering material of claim
 9. 14. A method for the cultivation of usefulcrops, which comprises cultivating said useful crops in a green housecovered with the agricultural covering material of claims 9, 10 or 11.